1. Field of the Invention
The present invention relates generally to magnetic heads for reading data written to storage media, and more particularly to magnetic read heads for disk drives.
2. Description of the Prior Art
A computer disk drive stores and retrieves data by positioning a magnetic read/write head over a rotating magnetic data storage disk. The head, or heads, which are typically arranged in stacks, read from or write data to concentric data tracks defined on surface of the disks which are also typically arranged in stacks. The heads are included in structures called “sliders” onto which the read/write sensors of the magnetic head are fabricated. The slider flies above the surface of the disks on a thin cushion of air, and the surface of the slider which faces the disks is called an Air Bearing Surface (ABS).
The goal in recent years is to increase the amount of data that can be stored on each hard disk. If data tracks can be made narrower, more tracks will fit on a disk surface, and more data can be stored on a given disk. The width of the tracks depends on the width of the read/write head used, and in recent years, track widths have decreased as the size of read/write heads has become progressively smaller. This decrease in track width has allowed for dramatic increases in the recording density and data storage of disks.
A magnetic recording head reads back the information stored in recording medium based on the mechanism that the read sensor's electrical resistance changes with the magnetic field of data bits formed on the data medium. A recording head sensor typically consists of, among other structures, a pinned magnetic layer and a free magnetic layer. The magnetic moment of free layer rotates in response to the external magnetic field, e.g., the magnetic field from the data bits of the recording medium. The magnetic orientation of the pinned layer, by contrast, should be fixed firmly. The magnitude of the read sensor's resistance change is determined by the relative angle between the magnetic moments of the free layer and the pinned layer.
The magnetic moment of the pinned layer is typically fixed by fabricating the pinned layer on an antiferromagnetic (AFM) pinning layer which fixes the magnetic moment of the pinned layer at an angle of 90 degrees to the air bearing surface (ABS).
The free layer material is a soft material, magnetically speaking, with low coercivity, which is a measure of the minimum field strength necessary to make changes in the orientation of the magnetic domains. The magnetic moment of the free layer is free to rotate laterally within the layer with respect to the ABS from a quiescent or zero bias point position in response to magnetic field flux from data bits located on the rotating magnetic disk. The sensitivity of the sensor is quantified as the magnetoresistive coefficient dr/R where dr is the change in resistance of the sensor from minimum resistance to maximum resistance and R is the resistance of the sensor at minimum resistance.
As referred to above, it is common practice in the art to pin the pinned layer by using a layer of anti-ferromagnetic (AFM) material, which is often referred to as the pinning layer. The magnetic orientation of the AFM pinning layer of the read sensors, and thus the orientation of the pinned layer, is set during the wafer fabrication, typically when the sensors are still in the form of continuous films. The sensor films are then processed to their final dimensions. In this processing, the left and right sides of the sensor are defined by ion milling, which thus defines the track width of the sensor. The rear side of the sensor is also defined by ion milling. The front face of the sensor, which faces the recording medium and which will be part of the Air Bearing Surface (ABS), is typically reduced to the operational dimension by a mechanical lapping process. The dimension of the front face to the rear side is known as the stripe height. Both the track width and stripe height are very important to the operating characteristics of the read head and are very tightly controlled during fabrication.
It has been discovered that while the pinning layers, (and hence the pinned layers) are well aligned when they are still in the full-film stage on the wafer, they are often misaligned when the sensors are reduced to the final dimensions. This misalignment may be caused by damage generated during the ion-milling and lapping processes, or by a re-definition of the magnetic domain boundary conditions of the small volume of material within the sensor. It is generally true that the smaller the sensor, the more serious the misalignment is. As the recording density becomes increasing higher, all the dimensions of the read sensor, stripe-height, width and thickness are being made smaller, and consequently the misalignment of the pinning layer is becoming a more serious problem.
Since the process of shaping the read sensor to its final dimensions can result in damage to that same sensor, it is desirable to set the direction of the pinning layer after the recording heads are already shaped to the final dimensions. The process used to set the magnetic orientation of the pinning layer is to anneal the heads at elevated temperature within a strong magnetic field oriented perpendicular to the ABS, along the intended direction of the magnetic orientation of the pinning layer.
Magnetic heads are embedded in structures called sliders. Finished sliders have a very smooth ABS and this smoothness is required for sliders to fly very low above the disk surface. As the name implies, the Air Bearing Surface, which faces the surface of the recording medium, flies on a cushion of air formed by the rotation of the disk surface near the magnetic head. The flying characteristics of the slider are very sensitive to the topography of this surface, and the slightest variation in the ABS can cause a magnetic head of the slider to fly too close to the surface, or too far away, or even to crash into the disk. Ideally, the process of setting the pinning direction by annealing would not interfere with the topography of the ABS. However, after annealing at elevated temperature, the slider surface may be distorted, due to the thermal cycle. Specifically, due to differing thermal expansion characteristics of different materials, protrusions may form in the ABS. These protrusions may interfere with the operation of the slider. It is of course possible to lap the ABS again to remove the protrusions, but this adds to processing time and may disorder the pinning direction all over again. ABS distortion is one of the major problems which interfere with the implementation of slider annealing when the sensors are in the final dimension.
Thus there is need for a method of fabrication which allows annealing of sensors in their final dimensions without producing ABS distortion.